David Spade shares photo of sister-in-law Kate Spade at his book signing [David Spade/Instagram ]

Alongside a photo of Kate smiling at one of his book signings he wrote: "Katy at my book signing. I love this pic of her. So pretty.

"I don’t think everyone knew how f*****g funny she was. It’s a rough world out there people. Try to hang on."

The 53-year-old shared another photo on Instagram of them at a family Christmas gathering.

Kate Spade has died at the age of 55 [Getty ]

"Fuzzy picture but I love it. Kate and I during family Christmas photos. We had so much fun that day. She was so sharp and quick on her feet. She could make me laugh so hard. I still can’t believe it. It’s a rough world out there people, try to hang on."

Kate Spade was pronounced dead at her apartment yesterday morning after being found by her housekeeper. She is thought to have taken her own life.

Most known for Kate Spade Handbags, which she co-created with husband Andy Spade in 1993, the designer owned hundreds of branches around the world.

Kate and husband Andy Spade [WireImage]

She sold the company in 2007 to take care of her daughter Frances Beatrix Spade, who was born in 2005.